hi, i´m 38 years old, i´ve never tried a windsurf board, but i bought an aquasport multiglide 4.1, few months ago. I don´t have no windsurf school near me, so i´ve been learning some basics with the multisport, as it as a lot of volume, i never have equilibrium problems, and learned how to gybe up and downwind easily, uphauling, and sailing upwind,normaly i sail in small lakes with winds 5-15 knots

right now, aquaglide is limiting me, so i want to buy a real board, i don´t know what board to buy, i was thinking in a GO155 2009 (550 eur) or an ISonic 125 2006 (400eur),

Do i have to pass through an easier step, like buying a big volume with dagger? such a bic core 293OD?

i weight 73-75 kg..

and usualy sail in small lakes with low wind speeds, 15-20 knots max..

A beginner / intermediate sailing on small lakes in about 10 knot: Yes, you should look for a board with a dagger (and absolutely NOT an iSonic 125).

A board like the Core 293D will take you from daggerboard lightwind sailing all the way to planing windsurfing and jibes. There are of course other good alternatives as well, like the Phantom Race 320. Or from other manufacturers a Kona One, or a Fanatic Viper, or a RRD Longrider, ...